BRIGHTON, England -- Three points on Brighton 3-2 Manchester United in the Premier League on Sunday afternoon.

1. Jose Mourinho warning appears true

Jose Mourinho said this season would be tough for Manchester United, but he probably did not expect to be proved right quite so quickly.

Through the summer and during the first week of the new Premier League season, he has painted a bleak picture of United's prospects. Even a 2-1 win over Leicester on opening night did little to improve his mood.

"I think it's going to be a very hard season," he said in an interview on Friday. And judging by the performance against Brighton at the AMEX on Sunday afternoon, it looks like he is right on the money.

In the space of two minutes and 23 seconds during the first half, United went from control to calamity. After 24 minutes, Solly March crossed from the left and Glenn Murray nipped in front of Victor Lindelof to cleverly clip his finish over David De Gea. Then from the re-start, Eric Bailly gave away a needless corner and some penalty box pinball ended with Shane Duffy scoring a second after expertly controlling Anthony Knockaert's miscued shot.

United came back from two goals down to win twice last season, and when Romelu Lukaku headed in his first goal of the season from close range it looked like it might be on again. But just as it looked like Mourinho's team were thinking about settling down, De Gea clipped a sloppy pass towards Fred in the centre of midfield, Dale Stephens slipped in Pascal Gross and Bailly brought him down. Gross got up to beat De Gea from the spot and the Brighton players trooped off at half-time with the fans singing "we want four."

It didn't come, but it didn't matter. Neither did Paul Pogba's late penalty after Duffy had brought down substitute Marouane Fellaini in stoppage time.

By the end the home supporters had changed their tune to: "Can we play you every week?" and "you're going down with the Palace."

It's not quite that bad for Mourinho but his preseason prediction is already coming true.

Manchester United were a shambles in defeat at Brighton. Dan Istitene/Getty Images

2. United's centre-backs a shambles

Mourinho wanted a central defender in the final weeks of the transfer window, and despite interest in Harry Maguire, Toby Alderweireld, Jerome Boateng and a host of others, nothing happened.

If the United manager wanted to make his point to Ed Woodward, he need only post of video of the first half here to the chief executive's office at Old Trafford.

He picked Lindelof and Bailly against Brighton, and after 45 minutes they had helped cost United three goals.

Lindelof was at fault for the first, letting Murray steal in to score. Bailly, not to be outdone, gave away a corner in the buildup to the second and then chopped down Gross in the box for Brighton's penalty just before half-time.

Both signed by Mourinho for a combined fee of £60 million, they have started the season as first choice, but it would be no surprise if they were both sat in the stands when Tottenham turn up at Old Trafford on Aug. 27.

For now, Mourinho will have to make do with what he has got. Chris Smalling, trusted to play nearly 50 games last season, was on the bench while Phil Jones, who started the FA Cup final in May, was not in the squad at all. Marcos Rojo is another option, but the Argentina defender is still nursing an injury picked up at the World Cup.

There are problems at the other end, too, and United managed just three shots on target while Lukaku was limited to just 24 touches all game.

Eric Bailly and Manchester United's defence had a nightmare on the south coast. Dan Istitene/Getty Images

3. Brighton off to a flyer, home form key

Brighton had the eighth best home record in the Premier League last season with seven of their nine wins coming at the AMEX. Their form on their own pitch will be key again is they are going to survive again, and Chris Hughton could not have asked for a better start. It was a 1-0 win over United here in May that secured their top-flight status last season, and this could turn out to be just as significant.

After the demoralising defeat at Watford on the opening weekend, it was vital that Brighton got up and running as quickly as possible. The Premier League can be an unforgiving place when you get stuck in a run of poor form, but Brighton can head to Liverpool on Saturday with confidence that they can upset Jurgen Klopp's side.

Only four teams managed to win at Brighton last season and it will be a difficult place to play this season, too. In a tight, compact arena, the fans can get on top of opposing teams, and Brighton gave them enough encouragement in the opening exchanges against United to get them into the game early.

If they can do that more often than not this season, they should win enough home games to stay in the league for a third successive campaign.